Rate Of Ca Release Research Articles

Decoupling the Ca release characteristics induced by O-containing functional groups during volatile-char interaction based on model compounds

Alkali metals and alkaline earth metals (AAEM) are important factors to be considered in coal gasification process, and understanding the release behavior of AAEM under the interaction of volatile-char is the key to realize efficient thermal conversion of coal. In this study, four typical O-containing functional groups (—COOH,—OH, CO,—OCH3) were used to react with coal char in a fixed-bed reactor, the reaction temperature was set up at 750，800，850，900 ℃ to survey the release characteristics of Ca by different oxygen functional groups during the interaction of volatile-char at different temperatures from a quantitative point of view. The result show that the Ca release rate of coal char is not high in the whole reaction temperature range, and the interaction of O-containing compounds-coal char at lower temperature will increase the O content (C—O and CO) of coal char, the content of Ca in interactive coal chars was higher than that of the coal char. At lower temperature, the order of compounds inhibiting Ca release ability is: C6H5CHO≈C6H5COOH > C10H8O2 > C6H5OCH3. In addition, it also seems that O-containing compounds (except C6H5COOH) can obviously promote the conversion of ammonium acetate-soluble Ca to water-soluble Ca during the interaction with char. As the temperature increases, the change trend of O-containing functional groups on the surface of sample after interaction is completely opposite to that at lower temperature, the O-containing model compounds undergo de-oxidation, cracking and polymerization in the effect of coal char and AAEM, causing the formation of polycyclic aromatic hydrocarbon on the surface of the char, which hinders the diffusion of Ca from the char to the gas phase. This work is good for enriching and developing the study on the release characteristics of alkali earth metals during the interaction of volatile-char, and provides a theoretical basis for the development of related industries.

Correlation between Ca Release and Osteoconduction by 3D-Printed Hydroxyapatite-Based Templates.

The application of hydroxyapatite (HA)-based templates is quite often seen in bone tissue engineering since that HA is an osteoconductive bioceramic material, which mimics the inorganic component of mineralized tissues. However, the reported osteoconductivity varies in vitro and in vivo, and the levels of calcium (Ca) release most favorable to osteoconduction have yet to be determined. In this study, HA-based templates were fabricated by melt-extrusion 3D-printing and characterized in order to determine a possible correlation between Ca release and osteoconduction. The HA-based templates were blended with poly(lactide-co-trimethylene carbonate) (PLATMC) at three different HA ratios: 10, 30, and 50%. The printability and physical properties of the HA templates were compared with those of pristine PLATMC. In vitro, osteoconductivity was assessed using seeded human bone marrow-derived mesenchymal stem cells. A mild rate of Ca release was observed for HA10 templates, which exhibited higher mineralized extracellular matrix (ECM) secretion than PLATMC at 14 and 21 days. In contrast, the high rate of Ca release exhibited by HA30 and HA50 templates was associated with reduced osteoconduction and impeded mineralized ECM secretion in vitro. Similar results were observed in vivo. In the calvarial defect model in rabbit, PLATMC and HA10 templates exhibited the highest amount of new bone formation, with obvious contact osteogenesis on their surfaces. In contrast, HA30 and HA50 exhibited distant osteogenesis and reduced amounts of new bone ingrowth. It is concluded that HA-based templates are osteoconductive only at low rates of Ca release.

Properties and release behavior of sodium alginate-based nanocomposite active films: Effects of particle size of IRMOF-3

Nanoparticles are used as fillers to improve the properties of biopolymers, and their particle size is an important parameter. This work aims to investigate the effect of particle size of isoreticular metal-organic framework-3 (IRMOF-3) on the mechanical, physical, and release properties of sodium alginate (SA)-based composite active film. In our study, IRMOF-3 with six different particle sizes was synthesized by introducing additives. IRMOF-3 loading with carvacrol (IRMOF-3/CA nanoparticles) was incorporated into the SA matrix to prepare the composite film. The characterization and testing results of films showed that the particle size of nanoparticles affected the physical morphology and chemical structure of the film. Especially smaller nanoparticles uniformly dispersed into the SA matrix more easily, forming a denser and more stable spatial network structure with SA, which could more significantly improve the tensile strength, water vapor barrier, and hydrophobic properties of the film (P < 0.05). In addition, the CA release rate from the active film could be significantly reduced by about 33.90 % even when the smallest particle size of the IRMOF-3/CA nanoparticles was added. Therefore, when IRMOF-3/CA is used as the nano-filler to develop SA-based active film, its particle size has a potential influence on the properties of the film.

Geochemical assessment of mineral sequestration of carbon dioxide in the midcontinent rift

AbstractThis study examines the potential of Midcontinent Rift rocks to facilitate long‐term CO2 sequestration by providing the necessary Ca and Mg for carbonate mineralization. Surface samples were collected from the Oronto and Bayfield‐Jacobsville Groups around Lake Superior and used for petrography and X‐ray diffraction to determine their mineral composition. Also, X‐ray fluorescence was also used to assess their bulk chemical composition. The samples were then exposed to CO2 and deionized water in Teflon‐lined vessels at 90°C, and the resulting leachate fluids were analyzed for the cation released during the testing. SEM microscopy was used to examine the samples for potential mineralization of carbonate minerals. The Oronto Group sediments consist primarily of feldspathic to feldspathic lithic arenites with a chlorite‐dominated matrix, and the primary porosity is blocked by calcite and hematite cement. The Bayfield–Jacobsville sequences are porous quartz arenites to feldspathic quartz arenites that do not contain significant accumulation of Ca‐, Mg‐, and Fe‐bearing minerals. The leachate fluids obtained from Oronto Group samples exhibit a maximum Ca release rate (5.2 × 10−4 mole/cm2.day), indicating rapid calcite cement dissolution and increased porosity and permeability. SEM/EDS microanalysis revealed areas where pore‐filling calcite was preferentially dissolved. Longer‐term rock‐water reactions resulted in induced carbonate mineralization, as evidenced by calcite crystals observed in a sample reacted for 102 days. © 2024 Society of Chemical Industry and John Wiley &amp; Sons, Ltd.

Influence of calcium chloride on the fine particulate matter formation during coal pyrolysis

This study investigated the influence of CaCl2 on fine particulate matter (PM0.5) formation during coal pyrolysis. Two acid-washed coals were loaded with different amount of CaCl2 by physical impregnation. Pyrolysis experiments were conducted in a flat-flame burner at 1400 K, 1600 K, and 1800 K. The PM0.5 yield was evaluated through the size-segregated sampling with a low pressure impactor (DLPI+). Then, the transformation properties of CaCl2 was analyzed with X-ray photoelectron spectroscopy (XPS) and inductively coupled plasma optical emission spectroscopy (ICP-OES). Finally, the soot properties were analyzed with transmission electron microscopy (TEM), Raman spectroscopy and Fourier transform infrared spectroscopy (FTIR). The results show that PM0.5 yield is affected by coal type, CaCl2 loading level, and pyrolysis temperature. Loading small amount of CaCl2 can reduce the PM0.5 yield through soot inhibition, while high loading of CaCl2 increases the PM0.5 yield by forming mineral particles, the lowest PM0.5 yield occurs at 1.5 % Ca content. The PM0.5 reduction rate of CaCl2 increases then decreases with temperature from 1400 K to 1800 K. On all tested conditions, the PM0.5 yield of low-rank Zhundong subbituminous coal was lower than Shenhua bituminous coal. The release rate of Ca into PM0.5 is positively related to pyrolysis temperature and CaCl2 loading level. Ca loading decreases the sizes of soot primary particles and agglomerates, and leads to smaller amorphous cores and more disordered graphitic shells in the soot primary particles. CaCl2 loading also causes the dealkylation and deoxygenation of soot. The influence of CaCl2 on soot formation can be summarized as the catalytic effect on soot precursor formation, the enhancement of soot nucleation, and the inhibition of soot coagulation.

Development and Characterization of a Novel Soil Amendment Based on Biomass Fly Ash Encapsulated in Calcium Alginate Microspheres.

Biomass fly ash (BFA) from a biomass cogeneration plant was encapsulated into calcium alginate microspheres (ALG/Ca) and characterized. An FTIR analysis indicated that BFA loading weakened molecular interactions between ALG/Ca constituents (mainly hydrogen bonding and electrostatic interactions), thus changing the crosslinking density. SEM and AFM analyses revealed a wrinkled and rough surface with elongated and distorted granules. The in vitro release of BFA’s main components (K, Ca, and Mg) was controlled by diffusion through the gel-like matrix, but the kinetics and released amounts differed significantly. The smaller released amounts and slower release rates of Ca and Mg compared to K resulted from the differences in the solubility of their minerals as well as from the interactions of divalent cations with alginate chains. The physicochemical properties of the novel microsphere formulation reveal significant potential for the prolonged delivery of nutrients to crops in a safe manner.

Dynamic behaviors of the sodium, calcium and iron release during coal combustion using multi-point LIBS

A novel application of multi-point LIBS was used to investigate the mineral release for dispersed-particle streams during coal combustion in an enclosed laminar flow reactor. A 1064 nm Nd: YAG laser was used to ablate the pulverized coal in air-like combustion environments at atmospheric pressure. The electron temperature (Te) and electron density (Ne) were calculated to evaluate the characteristics of the laser-induced plasma along the height from the burner surface, and LS-coupling method was further used to distinguish whether self-absorption occurred. The particle temperature was measured by a two-color pyrometer, and the time-resolved behaviors of Na, Ca and Fe along with the combustion process were measured by LIBS. Results show that the Te and Ne of laser-induced plasmas decreased with the flow of coal flame upon devolatilization, and became relatively stable during char combustion. There was little atomic self-absorption during char-combustion process, which provided theoretical support for quantitative combustion analysis. The Na release, mainly atomic forms, decreased with the particle flow upon devolatilization and showed a trend from rise to decline following devolatilization. The Fe and Ca was rarely released upon devolatilization. During char combustion, the Ca have a similar behavior to Na release, while the Fe increased and then remained constant. The temperature dependent kinetics of the Na and Ca release rate was found to obey an Arrhenius expression. The kinetics of Na and Ca atomic release determined by a first-order model had the pre-exponential factor of 101.16 and 102.67s−1 and the activation energy of 87.2 and 150.8 kJ/mol, respectively.

Release characteristics of AAEMs and physicochemical structural evolution of char during rapid coal pyrolysis

Rapid pyrolysis experiment of Zhundong coal was conducted in a high-frequency furnace to investigate release characteristics of alkali and alkaline earth metals (AAEMs) and its correlation with changes of physical and chemical properties of char. Residence time and atmosphere during pyrolysis were important process parameters that affected the migration characteristics of AAEMs and physicochemical structural evolution of char. Experimental results show that the release of AAEMs in coal char increases over time. The maximum release rate of Na, Mg and Ca is 61.05%, 64.47%, and 44.01%, respectively. Promoting effect of CO2 on release of Na mainly occurs in the initial stage of rapid pyrolysis, nevertheless the promoting effect on release of Mg and Ca mainly is in the middle and late stage. CO2 accelerates release of AAEMs by promoting release of volatiles, facilitating decomposition of oxygen-containing functional groups and aliphatic functional groups, and promoting formation of cracks on surface of coal char.

Dolomite dissolution mechanisms at acidic pH: New insights from high resolution pH-stat and mixed-flow reactor experiments associated to AFM and TEM observations

Recent studies of dolomite surface reactivity have shown that the processes controlling the dissolution of this mineral at the microscopic scale are still not well understood and quantified and not always consistent with the results of macroscopic observations. In the present study dolomite dissolution at pH 3 was investigated using both a macroscopic approach (pH-stat system and mixed-flow reactor) and microscopic characterization methods (atomic force and transmission electron microscopies) to quantify the release rates of Ca and Mg from bulk chemical analyses and determine the micro-topographical and chemo-structural changes that accompany the dissolution reaction.Dolomite dissolution rates from pH-stat and mixed-flow reactor experiments conducted on two distinct dolomite natural samples were found to differ by a factor of 2 between the two samples but falling within the range of values reported in the literature. High-resolution sampling of the aqueous fluid allowed observing frequent fluctuations of the Ca/Mg ratio (1.00 ≤ Ca/Mg ≤ 1.39) and its progressive decrease towards the stoichiometric value of the solid. Such oscillations are related, at the microscopic scale, to the preferential release of Ca from the fresh mineral surface, the concurrent generation of new surface that becomes exposed to the fluid and the temporary surface Mg enrichment occurring as the consequence of the faster departure of Ca ions to the aqueous solution. According to TEM observations, this dissolution mechanism does not bring about any noticeable modification of the dolomite surface structure in contact with the aqueous solution.Atomic force microscopy (AFM) experiments allowed observing the fast nucleation of high density etch pits during dissolution. The fluid effluent from the AFM cell was enriched in Ca (Ca/Mg =3.2–5.5) compared to the solution of the bulk experiments and the dolomite stoichiometry (Ca/Mg =1.01), but there was no evidence of formation of any Mg-rich secondary precipitate, contrary to what reported by previous studies with much higher Ca/Mg values. The increase of the Ca/Mg ratio in these effluents compared to the pH-stat and mixed-flow runs is likely related to the specific hydrodynamic conditions present within the AFM fluid-cell under transport-controlled dissolution regimes. The concentration of Ca aqueous ions preferentially released from the solid surface is likely further increased following their transport across the diffusive layer formed at the solid-fluid interface because of their higher diffusivity compared to aqueous Mg ions. However, the thermodynamic requirements for the formation of Mg-bearing secondary phases are unlikely to be met within this system under the investigated conditions.

Dynamics of Calcium, Magnesium, and Manganese During Litter Decomposition in Alpine Forest Aquatic and Terrestrial Ecosystems

Plant litter decomposition is one of the most important ecosystem processes influencing elemental biogeochemistry across terrestrial and aquatic environments. Calcium (Ca), magnesium (Mg), and manganese (Mn) are essential nutrients, which play a key role in plant energy metabolism, photosynthesis, and membrane transport of plants, and the major source of these nutrients is litter decomposition. Although litter decomposition has been subject to extensive research over the last several decades, the dynamics of Ca, Mg, and Mn in decomposing litter has been poorly assessed. Also, very few decomposition studies have been simultaneously carried out across aquatic and terrestrial ecosystems. Here, we conducted a two-year litterbag experiment across alpine forest aquatic (stream and riparian zone) and terrestrial (forest floor) ecosystems to address the dynamics of Ca, Mg, and Mn during litter decomposition. We found that (1) in general concentrations of Ca, Mg, and Mn all increased (that is, high immobilization) during the period of decomposition; (2) Ca and Mn immobilized in decomposing litter regardless of ecosystem type or litter species identity, while Mg showed release (mineralization) or immobilization depending on litter species identity; (3) a common hierarchy of drivers for Ca, Mg, or Mn release rate was found across all ecosystem types; and (4) Ca, Mg, and Mn concentrations all showed positive relationships with litter decomposition. Our results provide evidence of general patterns of Ca, Mg, and Mn dynamics in decomposing litter and significant positive effects of these nutrients on litter decomposition across terrestrial and aquatic environments associated with a forest ecosystem. We suggest that addressing nutrient dynamics across contrasting environments is crucial for predicting how biogeochemical cycling of different nutrients is modulated by litter mass decomposition.

Experimental study on mafic rock dissolution rates within CO2-seawater-rock systems

Far-from-equilibrium batch experiments have been performed to study the low temperature dissolution potential of crystalline submarine basalts (from Juan de Fuca Plate and Mid-Atlantic Ridges) and of a highly altered gabbro from the Troodos ophiolite (Cyprus) in presence of seawater and carbon dioxide (CO2). The experiments have been carried out at 40 °C for up to 20 days with initial pH of ∼4.8 and under ∼1 bar pCO2 to identify the progressive water-rock interactions. Elemental steady-state release rates from the rock samples have been determined for silicon and calcium, the solution concentrations of which were found to be the most effective monitors of rock dissolution. Mass balance calculations based on dissolved Si and Ca concentrations suggest the operation of reaction mechanisms focussed on the grain surfaces that are characteristic of incongruent dissolution. Also, basic kinetic modelling highlights the role of mass-transport limitations during the experiments. Ca release rates at pH ∼ 5 indicate significant contributions of plagioclase dissolution in all the rocks, with an additional contribution of amphibole dissolution in the altered gabbro. Si release rates of all solids are found to be similar to previously studied reactions between seawater and basaltic glass and crystalline basalt from Iceland, but are higher than rates measured for groundwater-crystalline basalt interaction systems. This comparison with previous experimental results resumes the debate on the role of experimental variables, such initial rock mass and crystallinity, pCO2, and fluid chemistry on dissolution processes. Our new data suggest that CO2-rich saline solutions react with mafic rocks at higher rates than fresh water with low pCO2, at the same pH. Most significantly, both ophiolitic gabbro and Juan de Fuca basalts show Si and Ca release rates similar or higher than unaltered crystalline basalt from Iceland, highlighting the potential substantial role that ophiolitic rocks and offshore mafic reservoirs could play for the geological storage of CO2.

Stimulating Ca&lt;sup&gt;2+&lt;/sup&gt; photoactivation of nerve cells by near-infrared light

Calcium ions (Ca&lt;sup&gt;2+&lt;/sup&gt;) play a key role of the nerve cells generating universal intracellular signals and controlling important functions. Ca&lt;sup&gt;2+&lt;/sup&gt; activation is of great significance for explaining the subcellular-level biological process. Light stimulated nerve cells to control intracellular signals and membrane activities has become a main method in neuroscience, and the photoactivation is one of the main ways to study intracellular Ca&lt;sup&gt;2+&lt;/sup&gt; transmission. Nerve cells can be directly stimulated by light to produce action potentials, but such techniques are inaccurate in the delivered light energy. To improve this, here in this work we show that gold nanorods (GNRs) can be conjugated to ligands to bound to human neuroblast cells (SH-SY5Y), and introduce an optical method of stimulating and monitoring Ca&lt;sup&gt;2+&lt;/sup&gt; signal in nerve cells in which the plasmonic excitation of GNRs is used. In this paper, we use confocal microscopy to display the 488 nm continuous wave laser irradiating SH-SY5Y cells with Ca&lt;sup&gt;2+&lt;/sup&gt; indicator (Fluo-4, AM) to check fluorescence. Near-infrared pulsed light at the plasmon resonance absorption peak of GNRs is used to stimulate Ca&lt;sup&gt;2+&lt;/sup&gt; signal transduction in SH-SY5Y labeled with GNRs, and Fluo-4, AM is used for two-photon excited fluorescence imaging. In addition, we use the pulsed laser with power of 0.5 mW and a wavelength of 800 nm. The Ca&lt;sup&gt;2+&lt;/sup&gt; activation can be achieved in 10 s on average. The release rate of Ca&lt;sup&gt;2+&lt;/sup&gt; from SH-SY5Y cells labeled with GNRs is 6 times that without GNRs. Next, in order to determine the source of changes in Ca&lt;sup&gt;2+&lt;/sup&gt;, we use the BPATA to deplete the intracellular Ca&lt;sup&gt;2+&lt;/sup&gt;, after 5 min, 200 μmol/L Ca&lt;sup&gt;2+&lt;/sup&gt; solution is added, and its Δ&lt;i&gt;F&lt;/i&gt;/&lt;i&gt;F&lt;/i&gt; is found to be more than 1.5 times that without GNRs. Thus, we believe that GNRs could enhance photoactivation through local surface plasmon resonance induced membrane depolarization and generate an action potential. The results prove the feasibility of using GNRs to enhance the activation of Ca&lt;sup&gt;2+&lt;/sup&gt; in nerve cells, and provide an optical means of lower photodamage and more precise for studying nerve cell ion channels. Our study demonstrates that enhancing photoactivation by GNRs could provide an outlook of basic research in neuroscience.

Lipophilization and molecular encapsulation of p-coumaric acid by amylose inclusion complex

p-Coumaric acid (CA) is a natural phenolic compound with a wide range of bioactivities, but its tendency to degrade during food processing and storage limits its application in functional foods. Forming amylose-guest inclusion complex is a technique to molecularly encapsulate guest molecules of interest and protect them from adverse environmental challenges. However, CA cannot be encapsulated into the helical cavity of amylose so this study used a strategy of lipophilization of CA to synthesize hexadecyl p-coumarate (HC), which might complex with amylose. The formation of the amylose inclusion complex was studied by complementary techniques: differential scanning calorimetry (DSC), X-ray diffraction (XRD), and Fourier transform infrared (FTIR) spectroscopy. To test the photo-stability of CA in the complex, a direct UV irradiation was performed. The in vitro release behavior of CA in the complex was also studied in both simulated gastric and intestinal fluids. The results showed that HC, but not CA, could form inclusion complex with amylose. Compared with CA, HC, and amylose-HC physical mixture, HC complexed with amylose showed a significant improvement in photo-stability (P < 0.05), with 90% retained, double the 43% retention of CA after 72 h of direct UV irradiation, and exhibited higher release rates of CA during in vitro digestion. These findings suggest that the amylose inclusion complex is a promising technique to protect CA in foods during processing and storage and to increase its bioaccessibility.

Contributions of Soil Meso- and Microfauna to Nutrient Release During Broadleaved Tree Litter Decomposition in the Changbai Mountains.

Soil meso- and microfauna (<2 mm in size) play an important role in the decomposition and nutrient release of litter. However, most research has focused on the influences of soil fauna on decomposition rates, while the impact of soil fauna on nutrient release has not been fully understood. We evaluated the influence of soil meso- and microfauna communities on nutrient release from decomposing Tilia amurensis Rupr. (Malvales:Tiliaceae) and Acer mono Maxim. (Sapindales:Aceraceae) leaves from the coniferous and broadleaved mixed forests of the Changbai Mountains. Litter decomposition and nutrient release were assessed using litterbags placed at the surface of the litter and using designs both with and without 2-mm mesh to either permit or exclude soil meso- and microfauna. The soil meso- and microfauna increased the decomposition of T. amurensis (not significantly) and A. mono (significantly, by 15%) litters. Presence of the soil meso- and microfauna accelerated the release rate of Mn in the A. mono litter by 59%, whereas it significantly decreased the release rates of Ca (in the T. amurensis litter) and P (in the A. mono litter) by 28 and 48%, respectively. These results suggest that a stronger understanding of the influence of soil fauna on nutrient cycling is necessary to understand the mechanisms of matter circulation.

Bioactivity of PLGA-gel-derived bioglass composites

A series of PLGA (poly L-lactide-co-glycolide) based composites modified with gel-derived glasses in the form of foils were obtained by solvent casting procedure. As a modifier, glass particles with different chemical compositions from the CaO–SiO2, CaO–P2O5–SiO2, and Al2O3–SiO2 systems were used. All glasses were synthesized by the sol-gel process. Evaluation of bioactive properties of obtained composites was made on the basis of surface changes occurring during contact with simulated body fluid. The changes of Ca, P and Si ions concentration in SBF after incubation of composites were also measured. The result showed that all composites with bioglasses (CaO–SiO2, CaO–P2O5–SiO2) exhibit formation of calcium phosphates layer after SBF test, however, kinetics of Ca, Si ion release and P uptake from SBF was dependent on bioglass chemical composition. The higher solubility, as well as faster consumption of phosphorus from SBF, was observed for materials from CaO–SiO2 (T1/PLGA, S1/PLGA) compared to composites with respective bioglass particles from the CaO–P2O5–SiO2(T2/PLGA, S2/PLGA). Our results showed that rate of Si and Ca release from the gel-derived glasses and P uptake from SBF are dependent on both: the concentration of respective ions in the materials and the presence of phosphates in their structure. For materials modified with gel-derived glasses from Al2O3–SiO2 system no significant surface changes during contact with SBF were observed, and it seems that their behavior in physiological solution indicate that they are bio-inert materials.

Phase evolution, microstructure and chemical stability of Ca1-xZr1-xGd2xTi2O7 (0.0 ≤ x ≤ 1.0) system for immobilizing nuclear waste

In order to ascertain the structural relationship of zirconolite and pyrochlore for their potential application in HLW immobilization, the Gd-doped zirconolite-pyrochlore composite ceramics (Ca1-xZr1-xGd2xTi2O7) were systematically synthesized with x = 0.0–1.0 by traditional solid-phase reaction method. The phase evolution and microstructure of the as-prepared samples have been elucidated by XRD and Rietveld refinement, Raman spectroscopy, BSE-EDS and HRTEM analysis. The results showed that zirconolite-2M, zirconolite-4M, perovskite and pyrochlore, four phases were identified in Ca1-xZr1-xGd2xTi2O7 system and could be coexisted at x = 0.4 composition. With the increase of Gd3+ substitution, the phase evolution was followed by zirconolite-2M→zirconolite-4M→pyrochlore. It is illustrated that the phase transformation from zirconolite-2M to zirconolite-4M was promoted by the preferential substitution of Gd3+ for Ca2+. And the solubility of Gd3+ in zirconolite-2M, zirconolite-4M and pyrochlore increased in sequence. The chemical stability test was also measured by the PCT leaching method. The normalized elemental release rates of Ca, Zr, Ti and Gd in Ca1-xZr1-xGd2xTi2O7 system were fairly low and in the range of 10−6−10−8 g m−2 d−1, which indicated a potential ceramics composite ensemble of CaZrTi2O7-Gd2Ti2O7 system for nuclear HLW immobilization.

The synthesis and chemical durability of Nd-doped single-phase zirconolite solid solutions

Nd-doped single-phase zirconolite solid solutions was synthesized by solid-state reaction and following two steps of acid treatment. The phase composition, microstructure, and chemical durability of the zirconolite solid solutions were investigated. About 15 at% Nd was successfully stabilized into the zirconolite. The element mapping images of Ca, Zr, Nd and Ti show that all the elements are almost distributed homogeneously in the zirconolite waste forms. Product Consistency Test (PCT) was conducted under different pH values (pH = 5, 7 and 9) to evaluate the chemical durability of the Nd-doped zirconolite waste forms. The normalized element release rate of Ca (LRCa) in pH = 5 medium is higher than that of pH = 7 and 9, while the LRNd value remains almost unchanged under different pH values. The LRNd value is as low as 10−5 g m−2 d−1 after 42 days.

Groundwater geochemistry in bench experiments simulating CO2 leakage from geological storage in the Newark Basin

To learn the effect of CO2 leakage on shallow drinking water aquifers, laboratory experiments were conducted to measure the chemical changes of aquifer water, in which the fine fraction of sedimentary rock from the Triassic Newark Basin Series were immersed. Elevated CO2 concentrations caused a decrease in pH, an increase in the concentrations of major ions including Ca, Mg, Si, K, and alkalinity, an enhanced dissolution of carbonate minerals, and an increase in the concentrations of trace elements including Mn, Fe, Be, Cr, Co, Cu, Zn, Rb, Zr, Cd, Sb, Ba, Pb, and U in water under both continuous CO2 flow and one-time injection batch experiments. The magnitude of concentration increase was significantly lower in batch experiments with one-time CO2 injection than in experiments with continuous CO2 flow, although less rigorous agitation was maintained in the batch experiment. The logarithmic elemental release rates of Ca, Mg, Si, Mn, Fe and Zn normalized by reactive surface area, when plotted together with those from field injection experiments, decreased with the increase of pH (or the decrease of log (pCO2)) following linear trends. The laboratory elemental release rates were 1-3 orders of magnitude higher than field injection experiment rates extrapolated to incubation pH conditions. Hydrogeochemical parameters including pH, major and trace elements, particularly Fe, Mn, Cd, Tl, and sulfate, can be used as early indicators for leakage detection and need to be monitored in compliance with the U.S. Environmental Protection Agency (EPA) drinking water regulations.

Transformation of alkali and alkaline-earth metals during coal oxy-fuel combustion in the presence of SO2 and H2O

The occurrence modes of alkali and alkaline-earth metals (AAEMs) in coal relate to their release behavior and ash formation during combustion. To better understand the transformation of AAEMs, the release behavior of water-soluble, HCl-soluble, HCl-insoluble AAEMs during Shenmu coal (SM coal) oxy-fuel combustion in the presence of SO2 and H2O in a drop-tube reactor was investigated through serial dissolution using H2O and HCl solutions. The results show that the release rates of AAEMs increase with an increase in temperature under the three atmospheres studied. The high release rates of Mg and Ca from SM coal are dependent on the high content of soluble Mg and Ca in SM coal. SO2 inhibits the release rates of AAEMs, while H2O promotes them. The effects of SO2 and H2O on the Na and K species are more evident than those on Mg and Ca species. All three types of AAEMs in coal can volatilize in the gas phase during coal combustion. The W-type AAEMs release excessively, whereas the release rates of I-type AAEMs are relatively lower. Different types of AAEM may interconvert through different pathways under certain conditions. Both SO2 and H2O promote the transformation reactions. The effect of SO2 was related to sulfate formation and the promotion by H2O occurs because of a decrease in the melting point of the solid as well as the reaction of H2O.

An experimental study on major element release from the sediments in the Changjiang (Yangtze River) Estuary

With the enhanced warming and acidification of global ocean, whether and to what extent the naturally-weathered fluvial sediment into the sea can release elements and thus influence the geochemical process and ecosystem of global ocean remain to be resolved. In this contribution, an experimental study was carried out to examine the release rates of major elements (Ca, K, Mg and Al) from the surface sediments in the Changjiang (Yangtze River) Estuary under the pH values of 4.0, 6.0 and 7.0. The two studied sediments consist primarily of quartz, plagioclase, calcite and clay minerals, with the BET (Brunauer, Emmett and Teller) surface areas of 61.7 m2 g−1 and 23.1 m2 g−1. Major elements of Ca, K, Mg and Al show different release rates under different solution pH values. With the decreasing solution pH, the release rates of Ca and K increase obviously, while the release rates of Mg and Al increase with the initial solution pH varying from 6.0 to 7.0. The different release rates of these elements are closely related to the original mineral composition of the sediments and the reaction kinetics. Based on the experimental observation, quartz and clay minerals that have low dissolution rates may dominate the major element release to the aqueous phase. This study reveals that the enhancing ocean acidification could cause considerable release of major elements from natural terrigenous sediments into the ambient marine environment, which has to be considered carefully in the future study on global change.